Catalyst deterioration diagnosis device

Abstract

To provide a catalyst deterioration diagnosis device capable of diagnosing deterioration of a catalyst even when an intake air amount detected by an air flow sensor deviates from an actual intake air amount.SOLUTION: A catalyst deterioration diagnosis device comprises: an air flow sensor 32 that detects an intake air amount taken in by an engine 2; an air-fuel ratio sensor 41 that detects an air-fuel ratio of exhaust gas flowing into a catalyst 42; an exhaust gas sensor 43 that can detect whether the air-fuel ratio of the exhaust gas flowing out from the catalyst 42 is rich or lean; an oxygen occlusion amount detection unit 101 that detects an amount of oxygen occluded in the catalyst 42 based on the intake air amount and the air-fuel ratio of the exhaust gas flowing into the catalyst 42; and an active air-fuel ratio control unit 102 that performs active air-fuel ratio control during deterioration diagnosis of the catalyst 42, and performs a correction to increase a rich side target value to match an actual intake air amount when an active air-fuel ratio control is executed when it is determined that the intake air amount detected by the air flow sensor 32 is larger than the actual intake air amount.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a catalyst deterioration diagnosis device.

Background Art

[0002] Patent Document 1 describes performing an accurate catalyst deterioration determination in consideration of the characteristics of the oxygen storage capacity of the catalyst.

[0003] By the way, at the time of diagnosing catalyst deterioration, active air-fuel ratio control is performed to alternately switch the air-fuel ratio of the exhaust gas flowing into the catalyst between rich and lean. When the oxygen storage amount of the catalyst reaches the rich-side target value, the air-fuel ratio is reversed from rich to lean, and when the oxygen storage amount of the catalyst reaches the lean-side target value, the air-fuel ratio is reversed from lean to rich.

[0004] The oxygen storage amount of the catalyst is calculated based on the intake air amount of the internal combustion engine detected by an air flow sensor, the air-fuel ratio of the exhaust gas flowing into the catalyst, and the target air-fuel ratio.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] When the intake air amount detected by the air flow sensor is larger than the actual intake air amount due to deterioration or detection error of the air flow sensor, the time for the oxygen storage amount of the catalyst to reach the rich-side target value decreases, and the lean-rich inversion cycle becomes shorter. As a result, there has been a problem that the output of the exhaust gas sensor on the downstream side of the catalyst does not reach a predetermined state, and the catalyst deterioration diagnosis cannot be performed.

[0007] Therefore, an object of the present invention is to provide a catalyst deterioration diagnosis device that can perform catalyst deterioration diagnosis even when the intake air amount detected by an air flow sensor deviates from the actual intake air amount.

Means for Solving the Problems

[0008] To solve the above problems, the present invention is a catalyst deterioration diagnosis device for diagnosing the deterioration of a catalyst disposed in an exhaust passage of an internal combustion engine, including an air flow sensor that detects the intake air amount inhaled by the internal combustion engine, an air-fuel ratio sensor that detects the air-fuel ratio of the exhaust gas flowing into the catalyst, an exhaust gas sensor that can detect whether the air-fuel ratio of the exhaust gas flowing out of the catalyst is rich or lean, an oxygen storage amount detection unit that detects the amount of oxygen stored in the catalyst based on the intake air amount and the air-fuel ratio of the exhaust gas flowing into the catalyst, and an active air-fuel ratio control unit that, when diagnosing the deterioration of the catalyst, alternately switches the air-fuel ratio of the exhaust gas flowing into the catalyst between rich and lean, reverses the air-fuel ratio to lean when the oxygen storage amount reaches the rich-side target value, and reverses the air-fuel ratio to rich when the oxygen storage amount reaches the lean-side target value. The active air-fuel ratio control unit performs a correction to increase the rich-side target value to match the actual intake air amount when executing the active air-fuel ratio control when it is determined that the intake air amount detected by the air flow sensor is larger than the actual intake air amount.

Effects of the Invention

[0009] Thus, according to the present invention, catalyst deterioration diagnosis can be performed even when the intake air amount detected by the air flow sensor deviates from the actual intake air amount.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

BEST MODE FOR CARRYING OUT THE INVENTION

[0011] A catalyst deterioration diagnosis apparatus according to an embodiment of the present invention is a catalyst deterioration diagnosis apparatus for diagnosing the deterioration of a catalyst disposed in an exhaust passage of an internal combustion engine, and includes an air flow sensor for detecting an intake air amount inhaled by the internal combustion engine, an air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas flowing into the catalyst, an exhaust gas sensor capable of detecting whether the air-fuel ratio of the exhaust gas flowing out of the catalyst is rich or lean, an oxygen storage amount detection unit for detecting an oxygen storage amount which is the amount of oxygen stored in the catalyst based on the intake air amount and the air-fuel ratio of the exhaust gas flowing into the catalyst, and an active air-fuel ratio control unit for alternately switching the air-fuel ratio of the exhaust gas flowing into the catalyst between rich and lean during the catalyst deterioration diagnosis, reversing the air-fuel ratio to lean when the oxygen storage amount reaches the rich-side target value, and reversing the air-fuel ratio to rich when the oxygen storage amount reaches the lean-side target value. The active air-fuel ratio control unit is configured to perform a correction to increase the rich-side target value to match the actual intake air amount when executing the active air-fuel ratio control when it is determined that the intake air amount detected by the air flow sensor is larger than the actual intake air amount.

[0012] Thereby, the catalyst deterioration diagnosis apparatus according to an embodiment of the present invention can perform the catalyst deterioration diagnosis even when the intake air amount detected by the air flow sensor deviates from the actual intake air amount.

EXAMPLE

[0013] Hereinafter, with reference to the drawings, a catalyst deterioration diagnosis apparatus according to an embodiment of the present invention will be described in detail.

[0014] In FIG. 1, a vehicle 1 equipped with a catalyst deterioration diagnosis apparatus according to an embodiment of the present invention includes an engine 2 as an internal combustion engine, an intake pipe 3, an exhaust pipe 4, and an ECU (Electronic Control Unit) 10.

[0015] In the engine 2, a cylinder 21 as a cylinder is formed. A piston 22 that can reciprocate up and down within the cylinder 21 is housed in the cylinder 21. Further, a combustion chamber 23 is provided above the cylinder 21.

[0016] The engine 2 is a so-called four-cycle gasoline engine that performs a series of four strokes including an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke while the piston 22 makes two reciprocations within the cylinder 21.

[0017] The piston 22 is connected to a crankshaft 2a via a connecting rod 24. The connecting rod 24 is configured to convert the reciprocating motion of the piston 22 into the rotational motion of the crankshaft 2a. The engine 2 is configured as a drive source of the vehicle 1.

[0018] The engine 2 is provided with a spark plug 25, an intake port 26, and an exhaust port 27. The spark plug 25 is fixed to the cylinder head with an electrode protruding into the combustion chamber 23, and its ignition timing is adjusted by the ECU 10.

[0019] An injector 28 is provided in the intake port 26. The injector 28 is a so-called port injection type fuel injection valve that injects fuel supplied from a fuel tank (not shown) by a fuel pump into the combustion chamber 23.

[0020] An intake port 26 communicates with an intake passage 3a in an intake pipe 3 described later. An intake valve 26a is provided in the intake port 26. The intake valve 26a is opened and closed so as to communicate or block the intake passage 3a and the combustion chamber 23.

[0021] An exhaust port 27 communicates with an exhaust passage 4a in an exhaust pipe 4 described later. An exhaust valve 27a is provided in the exhaust port 27. The exhaust valve 27a is opened and closed so as to communicate or block the exhaust passage 4a and the combustion chamber 23.

[0022] The intake pipe 3 is connected to the engine 2, and an intake passage 3a is formed inside. An air cleaner 31, an air flow sensor 32, and a throttle valve 33 are attached to the intake pipe 3 in order from the upstream side in the air intake direction.

[0023] The air cleaner 31 filters impurities such as dust contained in the intake air. The air flow sensor 32 is electrically connected to the ECU 10, detects the intake air amount which is the flow rate of the intake air flowing through the intake passage 3a, and outputs the detection result to the ECU 10. The throttle valve 33 is electrically connected to the ECU 10, and adjusts the intake air amount to the engine 2 by controlling the throttle opening according to a command signal from the ECU 10.

[0024] The exhaust pipe 4 is connected to the engine 2, and an exhaust passage 4a is formed inside. An air-fuel ratio sensor 41, a catalyst 42, and an exhaust gas sensor 43 are attached to the exhaust pipe 4 in order from the upstream side in the exhaust gas flow direction. The air-fuel ratio sensor 41 and the exhaust gas sensor 43 are arranged so as to sandwich the catalyst 42 in the exhaust pipe 4.

[0025] The air-fuel ratio sensor 41 is a sensor that detects the air-fuel ratio of the exhaust gas on the upstream side in the exhaust direction from the catalyst 42, and is constituted by, for example, an A / F sensor. The catalyst 42 is composed of a three-way catalyst that purifies exhaust gas.

[0026] The exhaust gas sensor 43 is a sensor that detects the air-fuel ratio of the exhaust gas on the downstream side in the exhaust direction from the catalyst 42, and is constituted by, for example, an O2 sensor.

[0027] The ECU 10 is constituted by a computer unit including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory for storing backup data and the like, an input port, and an output port.

[0028] In the ROM of the computer unit, a program for causing the computer unit to function as the ECU 10 is stored together with various constants, various maps, and the like. That is, when the CPU executes the program stored in the ROM using the RAM as a work area, the computer unit functions as the ECU 10 in the present embodiment.

[0029] In addition to the above-described air flow sensor 32, air-fuel ratio sensor 41, and exhaust gas sensor 43, various sensors such as a throttle sensor 11, a crank angle sensor 12, and a vehicle speed sensor 13 are connected to the ECU 10.

[0030] The throttle sensor 11 detects the throttle opening, which is the opening of the throttle valve 33. The crank angle sensor 12 detects the rotation angle of the crankshaft 2a of the engine 2 (hereinafter referred to as "crank angle"). The ECU 10 calculates the engine speed, which is the rotational speed of the engine 2, based on the information indicating the crank angle input from the crank angle sensor 12. The vehicle speed sensor 13 detects the vehicle speed, which is the speed of the vehicle 1.

[0031] Various devices such as an ignition plug 25, an injector 28, and a throttle valve 33 are connected to the ECU 10.

[0032] When a predetermined diagnostic condition is satisfied, the ECU 10 performs a deterioration diagnosis of the catalyst 42. As the predetermined diagnostic condition, it is stipulated that the engine operating region defined by the engine speed and the engine load is in a stable region where stable combustion can be ensured. In addition, it may be stipulated that the time change rate of each of the engine speed and the engine load is equal to or less than a certain amount as a predetermined diagnostic condition. Alternatively, it may be stipulated that satisfying the above two stipulations is a predetermined diagnostic condition.

[0033] When performing the deterioration diagnosis of the catalyst 42, the ECU 10 performs active air-fuel ratio control to alternately switch the air-fuel ratio of the exhaust gas flowing into the catalyst 42 between rich and lean.

[0034] For this reason, the ECU 10 includes an oxygen storage amount detection unit 101 and an active air-fuel ratio control unit 102.

[0035] The oxygen storage amount detection unit 101 detects the oxygen storage amount, which is the amount of oxygen stored by the catalyst 42, based on the intake air amount and the air-fuel ratio of the exhaust gas flowing into the catalyst 42.

[0036] As the oxygen storage amount, the oxygen storage amount detection unit 101 detects, for example, a relative O2 storage amount (hereinafter referred to as "relative O2S") calculated with reference to the start of diagnosis.

[0037] The relative O2S is calculated from the following formula using three parameters: the intake air amount (the detection value of the air flow sensor 32, hereinafter referred to as "Qa"), the detection value of the air-fuel ratio sensor 41 (hereinafter referred to as "AFreal"), and the target center A / F (hereinafter referred to as "AFtrgcent").

[0038]

Equation

[0039] During the deterioration diagnosis of the catalyst 42, the active air-fuel ratio control unit 102 alternately switches the air-fuel ratio of the exhaust gas flowing into the catalyst 42 between rich and lean. When the oxygen storage amount reaches the rich-side target value, the air-fuel ratio is reversed to lean, and when the oxygen storage amount reaches the lean-side target value, the air-fuel ratio is reversed to rich, thereby performing active air-fuel ratio control.

[0040] For example, the active air-fuel ratio control unit 102 determines the reversal timing from rich pulsation to lean pulsation or from lean pulsation to rich pulsation in the active air-fuel ratio control using the relative O2S as the oxygen storage amount detected by the oxygen storage amount detection unit 101.

[0041] During rich pulsation, when the relative O2S reaches the rich-side target value (determined by a control constant), the active air-fuel ratio control unit 102 reverses the feedback control from rich pulsation to lean pulsation. During lean pulsation, when the relative O2S reaches the lean-side target value, the active air-fuel ratio control unit 102 reverses the feedback control from lean pulsation to rich pulsation.

[0042] Therefore, in the active air-fuel ratio control, whether it is possible to ensure a perturbation time during which the deterioration of the catalyst 42 to be detected can be detected depends on the calculation accuracy of the relative O2S and the setting of the oxygen storage amount target values on the rich side and the lean side.

[0043] However, when the air flow sensor 32 deteriorates due to external factors or there are variations in sensor characteristics, a deviation occurs in Qa detected by the air flow sensor 32, resulting in a deviation in the calculation of the relative O2S. For this reason, it is assumed that an appropriate perturbation time cannot be obtained due to the deviation between the actual O2S and the relative O2S.

[0044] When Qa deviates to a side greater than the actual intake air amount, the integration of the relative O2S becomes faster than the actual O2S, and the reversal timing from rich pulsation to lean pulsation also becomes earlier. As a result, the behavior of the output signal of the exhaust gas sensor 43 changes, and the catalyst deterioration index may vary in a decreasing direction.

[0045] Similarly, when Qa shifts to the side where it is less than the actual intake air volume, depending on the progress of deterioration, the catalyst deterioration index may vary in the direction of increasing. That is, there is a concern that the deterioration or variation in characteristics of the air flow sensor 32 may affect the accuracy of the catalyst 42 deterioration diagnosis.

[0046] Note that there are also models that introduce an air flow sensor function diagnosis to detect the variation of the air flow sensor 32. The air flow sensor function diagnosis is configured to detect a failure when the difference between Qa and the estimated intake air volume (hereinafter referred to as "QthEST") calculated from the throttle opening is equal to or greater than a threshold value. When a failure is detected, the catalyst deterioration diagnosis is not performed. In the case of a deviation that does not result in a failure detection, since other function diagnoses are performed as usual, there is a concern about the impact on the aforementioned catalyst deterioration diagnosis accuracy.

[0047] Therefore, when the intake air volume detected by the air flow sensor 32 is more than the actual intake air volume, the active air-fuel ratio control unit 102 of this embodiment performs a correction to increase the rich-side target value to match the actual intake air volume during active air-fuel ratio control.

[0048] The active air-fuel ratio control unit 102, for example, calculates the deviation ratio Qa / QthEST every time the determination of the inversion from the lean oscillation to the rich oscillation of the feedback control is established after the start of the active air-fuel ratio control, and adds the correction value corresponding to the deviation ratio to the relative O2S target values on the rich side and the lean side, respectively.

[0049] The catalyst deterioration diagnosis process by the catalyst deterioration diagnosis device according to this embodiment configured as described above will be described with reference to FIG. 2. Note that the catalyst deterioration diagnosis process described below is started when the ECU 10 starts operating and is executed at a preset time interval.

[0050] In step S1, the active air-fuel ratio control unit 102 determines whether or not a predetermined diagnosis condition is satisfied.

[0051] When it is determined that the predetermined diagnostic condition is satisfied, the active air-fuel ratio control unit 102 executes the process of step S2. When it is determined that the predetermined diagnostic condition is not satisfied, the active air-fuel ratio control unit 102 executes the process of step S1.

[0052] In step S2, the active air-fuel ratio control unit 102 determines whether there is a detection deviation of the air flow sensor 32.

[0053] When it is determined that there is a detection deviation of the air flow sensor 32, the active air-fuel ratio control unit 102 executes the process of step S3. When it is determined that there is no detection deviation of the air flow sensor 32, the active air-fuel ratio control unit 102 executes the process of step S4.

[0054] In step S3, the active air-fuel ratio control unit 102 corrects the target oxygen storage amount for active air-fuel ratio control. After executing the process of step S3, the active air-fuel ratio control unit 102 executes the process of step S4.

[0055] In step S4, the active air-fuel ratio control unit 102 executes active air-fuel ratio control. After executing the process of step S4, the active air-fuel ratio control unit 102 executes the process of step S5.

[0056] In step S5, the active air-fuel ratio control unit 102 determines whether the oxygen storage amount is greater than the threshold value.

[0057] When it is determined that the oxygen storage amount is greater than the threshold value, the active air-fuel ratio control unit 102 executes the process of step S6. When it is determined that the oxygen storage amount is not greater than the threshold value, the active air-fuel ratio control unit 102 executes the process of step S7.

[0058] In step S6, the active air-fuel ratio control unit 102 determines that the catalyst 42 is normal. After executing the process of step S6, the active air-fuel ratio control unit 102 ends the catalyst deterioration diagnosis process.

[0059] In step S7, the active air-fuel ratio control unit 102 determines that the catalyst 42 is deteriorated. After executing the process of step S7, the active air-fuel ratio control unit 102 ends the catalyst deterioration diagnosis process.

[0060] The operation by such a catalyst deterioration diagnosis process will be described with reference to FIGS. 3 to 5. FIG. 3 shows the operation when using a deteriorated catalyst when there is no deviation in the detection value of the air flow sensor 32.

[0061] At time t1, the active air-fuel ratio control for catalyst deterioration determination is started, and the integration of the relative O2S is started.

[0062] At time t2, when the relative O2S reaches the lean-side target value, the fuel feedback control is reversed and shifted to rich pulsation.

[0063] At time t3, when the relative O2S reaches the rich-side target value, the fuel feedback control is reversed and shifted to lean pulsation.

[0064] Oxygen begins to be stored in the catalyst 42 by lean pulsation, and the output of the exhaust gas sensor 43 decreases as the oxygen that cannot be stored flows to the downstream side.

[0065] At time t4, as the output of the exhaust gas sensor 43 decreases to near the lean-side saturation voltage (for example, about 0.08 V), the deterioration index increases, and catalyst deterioration detection becomes possible.

[0066] FIG. 4 shows the conventional operation when using a deteriorated catalyst when the detection value of the air flow sensor 32 is deviated to the excessive side.

[0067] At time t11, the active air-fuel ratio control for catalyst deterioration determination is started, and the integration of the relative O2S is started.

[0068] Due to the detection deviation of the air flow sensor 32, the integration speed of the relative O2S increases. At time t12, the relative O2S reaches the lean-side target value, the fuel feedback control is reversed, and the operation shifts to rich oscillation.

[0069] The increase in the integration speed of the relative O2S shortens the time until the target value is reached, shortens the rich and lean oscillation times. At time t13, the relative O2S reaches the rich-side target value, the fuel feedback control is reversed, and the operation shifts to lean oscillation.

[0070] Due to the insufficient rich and lean oscillation times, the output of the exhaust gas sensor 43 does not drop completely even at time t14, which affects the deterioration index calculation.

[0071] Figure 5 shows the operation of this embodiment when using a deteriorated catalyst when the detected value of the air flow sensor 32 deviates to the excessive side.

[0072] At time t21, the active air-fuel ratio control for catalyst deterioration determination is started, and the integration of the relative O2S is started.

[0073] At time t22, the relative O2S reaches the lean-side target value, the fuel feedback control is reversed, and the operation shifts to rich oscillation.

[0074] The air quantity deviation rate Qa / QthEST is calculated at the timing of reversing from lean oscillation to rich oscillation at time t22. A correction value is calculated based on the calculated air quantity deviation rate. At time t23, a correction amount according to the air quantity deviation rate is added to the rich-side target value for correction.

[0075] At time t24, when the relative O2S reaches the rich-side target value, the fuel feedback control is reversed, and the operation shifts to lean oscillation.

[0076] Since the rich-side target value is corrected, rich and lean oscillation times are ensured. At time t25, the output of the exhaust gas sensor 43 decreases to near the lean-side saturation voltage, increasing the deterioration index and enabling catalyst deterioration detection.

[0077] Also, even when the relative O2S integration rate changes during diagnosis, at time t26, correction according to the air volume deviation rate is reflected, so that an optimal oscillation time can be ensured.

[0078] Thus, in this embodiment, when the intake air volume detected by the air flow sensor 32 is larger than the actual intake air volume, the active air-fuel ratio control unit 102 performs correction to increase the rich-side target value to match the actual intake air volume during active air-fuel ratio control.

[0079] Thereby, even when the integration rate of the oxygen storage amount changes due to the deviation between the intake air volume detected by the air flow sensor 32 and the actual intake air volume, the rich oscillation time and the lean oscillation time do not change. Therefore, the influence on the output signal of the exhaust gas sensor 43 on the downstream side of the catalyst 42 can be suppressed, and the accuracy and reproducibility of the catalyst deterioration diagnosis can be improved.

[0080] Therefore, even when the intake air volume detected by the air flow sensor 32 deviates from the actual intake air volume, the deterioration diagnosis of the catalyst 42 can be performed.

[0081] In this embodiment, an example has been described in which the ECU 10 makes various determinations and calculations based on various sensor information. However, the present invention is not limited to this. The vehicle 1 is provided with a communication unit capable of communicating with an external device such as an external server. Various determinations and calculations are performed by the external device based on the detection information of various sensors transmitted from the communication unit, and the determination results and calculation results are received by the communication unit, and various controls are performed using the received determination results and calculation results.

[0082] While embodiments of the present invention have been disclosed, it is obvious that modifications can be made by those skilled in the art without departing from the scope of the present invention. It is intended that all such modifications and equivalents be included in the following claims.

Description of Reference Numerals

[0083] 1 Vehicle 2 Engine (Internal Combustion Engine) 4a Exhaust Passage 10 ECU 11 Throttle Sensor 12 Crank Angle Sensor 13 Vehicle Speed Sensor 32 Airflow Sensor 41 Air-Fuel Ratio Sensor 42 Catalyst 43 Exhaust Gas Sensor 101 Oxygen Storage Amount Detection Unit 102 Active Air-Fuel Ratio Control Unit

Claims

【Claim 1】 A catalyst deterioration diagnosis device for diagnosing the deterioration of a catalyst disposed in an exhaust passage of an internal combustion engine, comprising: an air flow sensor for detecting an intake air amount inhaled by the internal combustion engine; an air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas flowing into the catalyst; an exhaust gas sensor capable of detecting whether the air-fuel ratio of exhaust gas flowing out of the catalyst is rich or lean; an oxygen storage amount detection unit for detecting an oxygen storage amount, which is the amount of oxygen stored in the catalyst, based on the intake air amount and the air-fuel ratio of the exhaust gas flowing into the catalyst; an active air-fuel ratio control unit that, when diagnosing the deterioration of the catalyst, alternately switches the air-fuel ratio of the exhaust gas flowing into the catalyst between rich and lean, and when the oxygen storage amount reaches a rich-side target value, reverses the air-fuel ratio to lean, and when the oxygen storage amount reaches a lean-side target value, reverses the air-fuel ratio to rich, and performs active air-fuel ratio control; wherein when the active air-fuel ratio control unit determines that the intake air amount detected by the air flow sensor is larger than the actual intake air amount, the active air-fuel ratio control unit corrects the rich-side target value to increase it to match the actual intake air amount during the execution of the active air-fuel ratio control.

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